Method of making a xerographic binder layer, and layer so prepared

ABSTRACT

A xerographic binder layer which comprises inorganic photoconductive particles contained in an insulating, fused, inorganic glass matrix, the photoconductive particles are present in an amount from about 1 to 25 percent by volume of the binder layer, and in the form of a plurality of continuous paths through the thickness of the layer. The method of making and imaging the binder layer is also described.

waited States atet [191 I Jones 1 Sept. 24, 19741 METHOD OF MAKING A XEROGRAPHIC BINDER LAYER, AND LAYER SO PREPARED [75] Inventor: Robert N. Jones, Fairport, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Oct. 16, 1972 [21] Appl. No.: 298,056

Related US. Application Data [63] Continuation-impart of Ser. No. 88,842, Nov. 12, 1970, abandoned, which is a continuation-impart of Ser. No. 627,664, April 3, 1967, abandoned.

117/34 [51] Int. Cl G03g 5/04, C23c 3/00 [58] Field of Search ..96/1.5, 1.8; 117/201, 34

[56] References Cited UNITED STATES PATENTS 3,151,982 10/1964 Corrsin 96/1 3,198,632 8/1965 Kimble 96/l.8 X 3,460,476 8/1969 Swigert et a1. 96/15 X 3,507,646 4/1970 Wood et a1. 96/15 X Primary ExaminerRonald H. Smith Assistant Examiner.lohn R. Miller [5 7 ABSTRACT 13 Claims, 3 Drawing Figures METHOD OF MAKING A XEROGRAPIIIC BINDER LAYER, AND LAYER SO PREPARED RELATED APPLICATIONS This application is a continuation-in-part of Applicants copending application, Ser. No. 88,842, filed Nov. 12, 1970, now abandoned which is a continuation-in-part of Applicants previously copending application, Ser. No. 627,664, filed Apr. 3, 1967, and now abandoned.

BACKGROUND OF THE INVENTION This invention relates to xerography and more specifically to a novel photosensitive member which employs a glass binder layer and a method of preparing such a member.

The art of xerography involves the use of a photosensitive element or plate containing a photoconductive insulating layer which is first uniformly electrostatically charged in order to sensitize its surface. The plate is then exposed to an image of activating electromagnetic radiation such as light, x-ray, or the like which selectively dissipates the charge in the exposed areas of the photoconductive insulator while leaving behind a latent electrostatic image in the non-exposed areas. This latent electrostatic image may then be developed and made visible by depositing a finely-divided, electroscopic marking particles on the surface of the photoconductive layer. This concept was originally disclosed by Carlson in US. Pat. No. 2,297,691, and is further amplified and described by many related patents in the field.

The discovery of the photoconductive insulating properties of highly purified vitreous selenium has resulted in this material becoming the standard in commercial reusable xerography. The photographic speed of this material is many times that of the prior art photoconductive insulating materials. Such a plate is characterized by being capable of receiving a satisfactory electrostatic charge and selectively dissipating such a However,. vitreous selenium suffers from two serious disadvantages: (1) its spectral response is very largely limited to the blue or near ultra-violet range; and (2) the preparation of uniform films of vitreous selenium has required highly involved and critical processes, particularly processes involving the preparation of extremely clean substrates and the requirement of vacuum deposition techniques. Also vitreous selenium layers are only meta-stable in that they are readily recrystallized to the inoperative crystalline form at temperatures only slightly in excess of those prevailing in conventional xerographic copying machines. These factors, together with the high cost of selenium itself has led, by commercial necessity, to the use of selenium xerographic plates only in repetitive processing cycles; that is, the selenium plate must be re-used many times in the xerographic process, so that the cost per copy of such a plate may be a reasonable small figure. Under conditions of optimum use, a vitreous selenium plate can be used to prepare 100,000 or even more copies before it deteriorates to the point of unsatisfactory image formation. Under less suitable conditions far fewer copies can be made. Because of these economical and commercial considerations, there has been a continuing effort towards developing photoconductive insulating materials other than selenium for use in the xerographic mode.

There has recently been developed a reusable xerographic plate comprising an inorganic photoconductive pigment dispersed in a glass binder. Plates of this type are described in detail by Corrsin in US. Pat. No. 3,151,982. Broadly, finely-divided inorganic photoconductive pigment particles are mixed with glass particles, usually in a liquid slurry, and the two-phase mixture or slurry coated onto a conductive substrate. The plate is then heated to fuse the glass particles into a substantially homogeneous matrix containing the photoconductive particles. These glass binder plates can be made to have an operating life many times greater than that of selenium and may be controlled to yield spectral sensitivities much greater than that of vitreous selenium xerographic plates.

Corrsin teaches that the particle size of the glass frit should be no more than 4 microns in diameter and that the photoconductor particle size may vary from 1 to 50 microns. A size of no more than about 1 micron is preferred for the photoconductor material. Corrsin, however, does not set forth any critical relationship between the glass frit and photoconductor particles.

The plates described by Corrsin generally have excellent physical characteristics in that they have specially smooth, tough surfaces adapted to easy cleaning and are unusually abrasion resistant. In order to produce a smooth surface, however, it is necessary to limit the percentage of photoconductive particles incorporated into the glass binder. Incorporation of a large proportion of photoconductor material produces a very rough surface which is not particularly suitable for reusable xerographic plates or drums. Additionally, since the plates are ordinarily made by mixing photoconductive particles with glass particles, followed by firing the glass, it is often difficult to obtain a uniform dispersion of the photoconductive particles throughout the glass binder. Often a two-phase layer is produced having surface areas or zones which differ in their photoresponse properties, and particularly in their rate of discharging surface electrostatic charge in response to impinging radiation. Certain areas are photoconductive and will dissipate surface charge by photoconductivity in response to impinging radiation. Other areas or zones, however, are non-photoconductive, and though capable of accepting and maintaining an electrostatic charge for a sufiicient time to produce xerographic images, do not dissipate such surface charge by photoconductivity, but dissipate the charge by another mechanism, as yet not completely understood. This characteristic of non-uniform or varying discharge rate across the surface of the photoreceptor promotes the retention of residual surface charge in areas where surface charge should be completely, or substantially completely, dissipated either by a photoconductive or nonphotoconductive mechanism, as the case may be. Such a condition simultaneously decreases the resolution capability of the xerographic plate while substantially increasing the background density. These areas result from matrix particles of a size which exceed the resolution capabilities of the development system. In addition, the employment of matrix particles having a size close to that of the photoconductor, i.e., less than a factor of 5 difference in the mean diameter, negates the desired geometry control and can result in the coalesence in firing of a number of these small particles into areas which are larger than the resolving capability of the development system. This result is analogous to the employment of larger matrix particles.

in the glass binder system described by Corrsin, the dispersion of the photoconductor particles throughout the non-photoconductive glass matrix should be relatively uniform. Inasmuch as the glass matrix is substantially non-photoconducting, there is little or no charge transport within the glass matrix of photo-injected charge carriers which are generated by the photoconductor particles upon exposure to activating radiation. It has been found that in these binder systems, the photoconductor particles must be in substantial continuous particle-to-particle contact throughout the thickness of the binder layer in order to insure the charge dissipationnecessary for rapid cyclic operation. To insure particle-to-particle contact, however, a relatively high volume concentration of photoconductor is required. This photoconductor concentration must be up to about 50 percent by volume, although some particleto-particle contact is observed at about 30 percent by volume. One disadvantage of high photoconductor loadings, however, is that the physical continuity of the glass matrix is destroyed, thereby significantly impairing the mechanical properties of the binder layer.

The optimum volume concentration ratio of photoconductor to glass binder material in these systems is therefore a compromise between photosensitivity and residual level on the one hand, and the mechanical properties on the other. The actual optimum volume ratio for any specific system is dependent, in general, upon the particle size and density of the photoconductor and the density and rheological properties of the glass binder material in relation to the photoconductor.

It has now been discovered that the optimum volume concentration of a photoconductor in the glass binder systems, such as those illustrated above, can be reduced significantly without sacrificing photosensitivity, if the bulk geometry can be controlled to insure substantial particle-to-particle contact of the photoconductor particles throughout the thickness of the glass binder layer. Such a reduction in photoconductor concentration should result in enhanced mechanical and surface properties, as well as improved control of the electrical characteristics of the glass binder layer.

OBJECTS OF THE INVENTION It is, therefore, an object of this invention to provide a novel photosensitive element which overcomes the above noted disadvantages.

It is, therefore, another object of this invention to provide an improved xerographic plate.

It is a further object of this invention to provide a glass binder xerographic plate having enhanced xerographic properties.

It is a further object of this invention to provide a glass binder xerographic plate having improved resolution capabilities while producing a copy having reduced background density.

A still further object of the present invention is to provide a method for the production of an improved glass binder xerographic plate.

Yet a still further object of the present invention is to provide a method for producing a glass binder xerographic plate having increased resolution capabilities while reducing background density.

The above and still further objects, features. and advantages of the present invention will become apparent upon consideration of the following detailed disclosure of specific exemplary embodiments of the present invention.

SUMMARY OF THE INVENTION In accordance with the instant invention, an improved glass binder photoreceptor is attained by employing a non-photoconductive glass binder or a matrix material in particulate form having a critically con trolled size range, and physically mixing the glass particles with a particulate photoconductor material also having a certain critically controlled size range. The glass matrix material and photoconductor particles are then formed into a permanent binder layer by fusing the glass particles together by heating to form a binder layer in which the dispersion of photoconductor particles is characterized by continuous paths of contacting photoconductor particles contained in a substantially continuous glass binder matrix. Thus by controlling the geometry of the binder layer, greatly improved electrical characteristics and mechanical properties can be attained. The instant invention also allows for a wider latitude in the choice of both the giass binder material as well as the photoconductor. The invention therefore eliminates the necessity to compromise between the electrical characteristics and mechanical properties of a xerographic binder layer, making these essentially independently controlled parameters.

An important step in the instant invention involves the photoconductor geometry control which is achieved by employing a particulate glass binder and photoconductor material having a critical size distribution with respect to each other. This concept may be illustrated by the following example: A photoconductive binder layer is made by forming a particulate mixture of photoconductive particles having a size distribution of about 0.001 to 2.0 microns with an inorganic, non-photoconductive, glass frit having a size distribution of about 0.l to microns. The photoconductor is present in a concentration from about 1 to 25 percent by volume. The mixture is dispersed in a suitable fluid carrier, such as water, in which neither the photoconductor nor glass frit is soluble. The dispersion or slurry is coated onto a bstrate and the carrier liquid allowed to evaporate. Thedried layer is then heated to fuse the glass particles into a continuous glass matrix containing photoconductor particles in the form of continuous paths in particle-to-particle contact throughout the thickness of the glass binder layer. The size of the glass particles should, in general, be at least about five times that of the photoconductor particles. This size relationship is necessary in order to force the photoconductor particles into the intersticies of the larger glass binder particles. Upon firing, the larger glass particles are fused and coalesce into a continuous matrix having a plurality of continuous photoconductive paths contained in the glass matrix. It should be noted that if the particle size of the photoconductor approaches that of the glass frit, the desired geometry of the photoconductor particles cannot be achieved and the photoconductor particles become completely encased in the binder matrix. In this case, the desirable results of the Applicant's invention are not achieved, as will be shown later.

Binder layers of the controlled dispersion type described above exhibit a combination of electrical characteristics and mechanical properties which are superior to those of the glass binder systems as exemplified by the examples described in the above mentioned Corrsin patent.

BRIEF DESCRIPTION OF THE DRAWINGS In general, the advantages of the improved structure and method in the instant invention will become apparent upon consideration of the following disclosure of the invention; especially when taken in conjunction with the accompanying drawings wherein:

FIG. I graphically illustrates the relationship between interstitial volume and varying glass matrix particle sizes.

FIG. 2A illustrates one embodiment of a photoconductive binder structure according to the instant invention.

FIG. 23 illustrates one embodiment of a particulate dispersion suitable for forming the structure of FIG. 2A.

DETAILED DESCRIPTION OF THE DRAWINGS According to the instant invention, a photosensitive glass binder layer having a controlled geometry is achieved by utilizing a glass frit in particulate form with photoconductor particles significantly smaller in size than the glass particles, thereby forcing the photoconductor to occupy the interstitial space of the packed glass particles. Upon firing, the larger glass particles are fused together to form a continuous glass matrix containing a network of photoconductive material in the form of a plurality of interlocking photoconductive paths throughout the glass matrix. This concept may be illustrated by the following discussion:

A coating cast from a dispersion of spherical matrix particles may be thought of as a system of closely packed spheres. The interstitial volume of such a layer will depend therefore on the size distribution of the particles and the type of packing. Hexagonal close packing of monospheres would result, therefore, in an interstitial volume of 47 percent of the total volume. Monospheres of a photoconductor material can be used to fill this 47 percent pore space without affecting the total volume, if the diameter of the photoconductor particles are sufficiently small in comparison to the diameter of the resin particles. If the packing of these photoconductor particles in the matrix pore space is also hexagonal-close-packed, the interstitial volume of the photoconductor will be in turn 47 percent of the total matrix interstitial volume. Since in this example approximately 50 percent of the layer volume comprises glass matrix particles, and 50 percent of the remaining volume is filled with photoconductor, a photoconductor volume concentration of about 25 percent of the initial layer volume will result. After evaporation of the carrier liquid and coalescence of the binder particles, such as by heating, the volume concentration of the photoconductor particles in the layer is 33 percent. More importantly, in this situation all of the photoconductor particles are in electrical contact from the top surface of the layer to the substrate in the same manner as achieved at 50 percent volume loading in the uniform dispersion case. This amounts to a reduction in required photoconductor volume concentration of 33 percent.

The concentration of photoconductor necessary to form continuous electronic pathways is therefore dependent on the interstitial volume of the matrix which is in turn critically dependent on the frequency of matrix particles of varying size and the magnitude of the size distribution as well as the particle shape. FIG. 1 illustrates the former effect where the pore volume can be reduced to about 17, 5, and 3 percent by utilizing glass matrix particles of vastly differing size having four. three, and two components, respectively. In these cases only about 8.5, 2.5 and 1.5 percent, respectively, by volume photoconductor would be necessary to form the desired continuous electronic pathways. FIG. I also illustrates that a low interstitial volume is also obtained by increasing the number of different sizes of particles in the distribution. It would therefore be possible in the idealized case to form a matrix system with an interstitial volume of 3 percent (four components) which would require only 1.5 percent by volume photoconductor to achieve the maximum number of continuous pathways.

Real particulate packing systems are of course much more complex since seldom are the individual particles spherical or for that matter of constant shape, and the frequency of sizes and the magnitude of the size distribution is normally the natural result of the preparation method, i.e., formation or grinding technique. It may also be obvious that in utilizing this particulate matrix geometry control approach in the fabrication of photoreceptor devices, the upper limit of particle size for the matrix may not exceed the resolution capability of the xerographic development system to be employed, and that the photoconductor size must be sufficiently smaller than the smallest matrix particle such that it can occupy the interstitial volume of the packing of this smallest size.

The optimum volume concentration of photoconductor to be employed in fabricating a photoreceptor is dependent therefore on the particle size, magnitude and type of size distribution, particle shape of both photoconductor and matrix, the size difference between the two, and the resolution capabilities of the xerographic development system. 1

In the practice of fabricating a practical xerographic photoreceptor device it has been determined that a preferred maximum size for glass matrix particles is about 10 microns. Particles above about 10 microns result in some image background, although a material having a very wide size distribution is not detrimentally affected by a small percentage by number of particles as large as about microns. The lower size limit of the matrix is again defined by the size of the photoconductor to be employed, but in a practical system would be in the range of about 0.1 micron. The range of the photoconductor particle size would in turn be from about 0.001 to 2 microns depending on the magnitude and shape of the size distribution. The minimum photoconductor concentration which might be employed, therefore, would be about 1 percent by volume, and the maximum about 25 percent, with most real materials showing an optimum in mechanical and electrical characteristics in the range of about 3 to 15 percent by volume.

A particularly preferred size range which insures an optimum of both electrical characteristics and physical properties consists of a glass frit particle size of about 1 to 10 microns used in conjunction with a photoconductor particle size range of about 0.001 to l micron, while maintaining the mean or average particle size of the glass frit at least five times greater than the mean or average particle size of the photoconductor particles.

The matrix particles determine the number and spacing of chain or pathway ends per unit area in the light absorption region at the photoconductor surface. As previously stated, the upper limit of the matrix particle size may not exceed the resolution capability of the xerographic development system used in conjunction with plates of the instant invention. Further, the photoconductor particle size must be enough smaller than the smallest matrix particle to occupy the interstitial volume in a packing of this smallest size. The ratio of the size of the glass matrix particles to the photoconductive particles should therefore be at least about to l and preferably about 100 to 1 or greater as can be seen from FIG. 1.

As stated above, the maximum size of glass frit particles which may be employed in the instant invention is dependent upon the resolution capabilities of the associated xerographic development system. For example, cascade development as described in US. Pat. Nos. 2,618,551, 2,618,552, and 2,638,416, can easily attain a resolution capability of about line pairs per millimeter, which corresponds to a dot approximately 33 microns in diameter; i.e., the minimum dot diameter which can be resolved by this development system. Therefore, the maximum size of binder particles which can be used in forming the matrix should be less than about 33 microns for cascade development. The table below lists five representative development systems with their respective normally achieved resolution capability in line pairs per millimeter and in microns. It should be understood that similar determinations can be made for other xerographic development systems.

In a preferred embodiment, the glass binder particles should be maintained at about one half or less the diameter of the maximum size listed for each development system in Table I. At diameters of one half or less, the lowest background density possible is attained for images made from photoreceptors of the present invention. These values in microns are about l6, 12, 35, 25 and 4 for cascade, magnetic brush, liquid gravure, aqueous and powder cloud development systems, respectively. It should also be understood that even with this preferred embodiment, the ratio of the size of the glass to photoconductive particles should be at least about 5 to l, and preferably about 100 to 1 or greater.

TABLE I Normally Achieved Normally Resolution Achieved (line pairs Resolution Development System per millimeter) In Microns Cascade 15 33 Magnetic Brush Liquid Gravurc 6-7 70 Aqueous 6-10 50 Powder Cloud 60 ll FIG. 2A illustrates one embodiment of a xerographic binder plate 10 of the instant invention and comprises a binder layer 11 supported on substrate 12. The binder layer 11 comprises photoconductive particles 13 dispersed in a non-uniform or controlled manner to form continuous paths throughout the binder layer thick ness, contained in a glass matrix 14. The volume con centration for this illustration is about 10 percent. The structure is formed from an initial dispersion of photo conductive particles having a mean size of 0.5 microns with a distribution of from 0.01 to 0.8 microns and a particulate binder material having a mean size of 5 microns with a distribution of about I to l2 microns. This dispersion, which is coated onto a supporting substrate, insures that continuous photoconductive paths are formed throughout the binder layer thickness. FIG. 28 illustrates the particulate photoconductor-binder dispersion prior to forming the structure of FIG. 2A. In FIG. 2B, glass binder particles 14 are considerably larger than photoconductor particles i5 and are dis persed in a liquid carrier (not shown). The dispersion is coated onto a supporting substrate 12 and the liquid carrier evaporated off. The dried layer shown by FIG. 28 results in a series of larger glass binder particles having their interstices filled with relatively smaller photoconductive particles 15. it can be seen by FIG. 2B, which is representative of the instant invention, that the volume occupancy of the photoconductor particles is restricted to the interstices of the larger matrix binder particles.

The binder layers of the instant invention may utilize any suitable inorganic photoconductive material and mixtures thereof. These include in any suitable inorganic materials which are sold specifically as pigments, photoconductors, or phosphors.

Typical inorganic photoconductors suitable for use in the instant invention comprise cadmium sulfide, cadmium sulfoselenide, cadmium selenide, zinc sulfide, zinc selenide, arsenic sulfide, lead oxide, zinc oxide, antimony trisulfide and mixtures thereof. US. Pat. No. 3,151,982 to Corrsin provides a more complete listing of inorganic photoconductors which may be used in the instant invention.

In addition, various additives, activators, dopants, and/or sensitizers may also be used to enhance the photoconductivity of the above photoconductive materialsv Zinc oxide exhibits enhanced spectral response when sensitized with a suitable dye. It is also well known that increased photosensitivity is obtained when photoconductors such as cadmium sulfide are reacted with a very small amount of an activator material such as copper.

The photoconductor concentrations may vary from as low as about 1 percent by volume to about 25 percent by volume of the binder layer. A photoconductor concentration of about 3 to 15 percent by volume, however, is preferred in that it generally insures the op timum combination of electrical characteristics and xe rographic properties.

The glass binder may be broadly defined as a highly insulating fused inorganic non-photoconductive glass, and is made up in various combinations of the three types of basic oxides used in making frits: acidic, basic and neutral or amphoteric. These glasses are adequately defined in the patent to Corrsin mentioned above, and are made up from compositions generally selected from the ranges set forth in Table 11 below.

TABLE II for a time sufficient to fuse the glass-binder particles B203 50 and then the coated drum is slowly cooled to room tem- J 20-75 perature. 395 040 The drums are placed in a Xerox 813 Office Copier ZnO l075 employing a cascade development system. Each drum S88 is given a uniform electrostatic charge in the dark and Na O exposed to a pattern or light and shadow whereby an if? I electrostatic latent image is formed on the photorecep- NaF 0-10 tor surface. Xerographic prints are made from each of fig 83 these Examples using cascade development. A compariof, o ison of the prints indicates that the lowest background density is obtained with Example I and that background Combined.

density increases with increasing Example number. It should be pointed out these ranges of compositions That Prints Obtained from Example III have ig may be varied and modified as would b b i t background density than prints obtained from Examthose skilled in the art. ples I and II but lower background density than prints Two specific glass compositions which are illustrative Obt e o Ex mp IV and of those contemplated by this invention are listed This above described background effect results from below in Table 111. These compositions are in weight 20 the fact that in Example I the relative mean size of the percent. glass particles is greater-than five times the mean size TAELE III GLASS BINDER COMPOSITIONS Sample CaO sio Na O 13,0 PbO CdO F U Tao zro B210 A1 0. K20

l. Pemco Commer- 2.5 45 14 7 15 4.0 3.4 2.4 6.0 0.5 0.2

cial rm H3172 2. Harshaw Commer- 18.5 .05 8.4 65 7.9 .07 .02 .01 0.05 cial frit N862 The glass binder layer may be supported on any conof the photoconductive particles (12 times), and furvenient electrical ground or backing plate. Typical mather, that the largest glass particle 10 microns) is sigterials include aluminum, brass, stainless steel, copper, nificantly below the resolving power of the cascade de- 4 nickel, zinc, or conductively coated glass. velopment system, which is 33 microns. In Example 11, DESCRIPTION OF THE PREFERRED the largesthglass pagticclie isl still bilowtthe rclrlsplvipg EMBODIMENTS power 0 e casca e eve opmen sys em w ie e ratio of the mean glass particle size to that of the photo- T following Examples are given enable those sensitive particles has decreased to 8 to l,which is very skilled in the art to mo e c y undersland and W 40 close to the minimum ratio of at least 5 to 1. This is furl h mventlon' They Should considered not as a ther illustrated by Example 111 where the 5 to 1 ratio of limitation upon the scope of the invention but merely glass to photoconductor particles has not been as bemg lnustratwe thereof achieved. In Examples IV and V, while the ratio of glass EXAMPLES v to photoconductor particles of at least 5 to 1 has been maintained, the largest size glass particles (45 microns) exceed the 33 micron resolving power of the cascade development system. As stated above, as the examples increase in number, the background density increases because of the deviation of the higher numbered examples from the particle size limitations of the present invention.

A mixture of glass binder particles having the composition of Sample 1 in Table III is ground to a particle size distribution of 0.1 to 45 microns using a Majac fluid energy mill. The mixture is separated into two fractions. One fraction is designated Example IV, and the remaining'fraction divided into four subfractions using an air classifier. These subfractions are designated Examples 1, 11,111, and V, respectively. EXAMPLES V] X I. 1-10 microns (mean size by wt. 6 microns) [L microns (mean size by wt 4 microns) Examples I-V are repeated using the glass composition of Sample 2 in Table III and using the same particle size distribution except that these coatings are fired at i gg sg gz iizz zf g 1,100: for 3 minutes. The results of Examples I-V are veri ie V. 10-45 microns (mean size by wt. 29 microns) To each fraction or subfraction there is added approxi- EXAMPLES XI-XW mately 10 percent by volume of photocond cti e Cad- Using an Alpine classifier and the glass composition mium sulfoselenide, having a mean particle size of 0.5 of Sample 1 in Table III, the following four fractions of microns and a size distribution of 0.01 to 0.8 microns. glass-binder particles are Obta ned Each dispersion is coated onto a clean cylindrical stain- X1. 3-8 microns (mean size by wt. 6 microns) less steel drum to form a final thickness of about 50 mi- X11. 0.1-8 microns (mean size by wt. 4 microns) crons, and then permitted to dry. Before cracking be- XIII. 0.1-3 microns (mean size by wt. 1.0 migins. the plate is fired at about 1,200F for 3 minutes crons) XIV. 8-45 microns (mean size by wt. 27 microns) Using alcohol as the dispersion medium, a slurry is prepared containing about lO percent by volume of photoconductive cadmium sulfoselenide, having a mean particle size of 0.5 microns and a size distribution of about 0.01 to 0.8 microns. Xerographic plates and prints therefrom are prepared as in Examples l-V except that the dispersion is coated onto a flat stainless steel plate rather than a cylindrical drum. A comparison of the prints indicated that the lowest background density is obtained with Example Xi and that background density increases with increased Example number.

EXAMPLE XV A coating slurry is prepared by first mixing 90 parts by volume of the glass composition of Sample 2 of Table III, having a mean size of 6 microns and a size distribution of about 3 to 8 microns, with parts by volume of photoconductive cadmium sulfoselenide, having a mean size of 0.5 microns and a size distribution of about 0.01 to 0.8 microns. Using alcohol as the dispersion medium, a coating slurry is formed with the glass and photoconductor particles. The slurry is then flow coated onto a 0.008 inch thick stainless steel sleeve 4 inches in diameter and 9 inches long to form a dried coating after firing of about 35 microns. The coating is dried at room temperature for 5 minutes and fired for 2 minutes at 677C.

The sleeve containing the photosensitive glass binder layer is then fitted over an aluminum drum blank 4 inches in diameter and 9 inches long to form a photosensitive glass binder drum. The drum is then placed in a Xerox 813 Office Copier and cycled to form an image by the basic steps of charging, exposure to imaging light to form a latent electrostatic image, development of the image with toner particles, transfer of the image to a sheet of paper, and fixing the image to form a permanent copy.

The plate is cycled 60,000 times under varying humidity conditions of 20, 40, 60 and 85 percent relative humidity. Throughout the testing, the resolution, which was good, remained constant until about 60,000 copies. The image density also remained high throughout the cycling. In addition, the drum exhibited good resistance to machine wear, as compared to vitreous selenium which is less stable to such cycling conditions.

In summary, it may be said that plates and drums of the instant invention exhibited high speed, good resolution and low background under cycling conditions and show marked improvement over similar glass binder photoreceptors which cannot insure the controlled geometry of the instant invention.

While the invention has been described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in the form and details may be made without departing from the true spirit and scope of the invention. Further, provided the advantageous results of this invention are not adversely effected, additional operations may be formed to achieve the herein disclosed results, or in certain circumstances, certain operations may be deleted as will be apparent to those skilled in the art. Numerous modifications may be made to adapt a particular situation or material to the teachings of the herein disclosed invention. All such additions, deletions. mod ifications, etc. are considered to be within the scope of the present invention.

What is claimed is:

l. A method of making a xerographic binder layer which comprises:

a. forming a particulate mixture of an inorganic glass frit and an inorganic photoconductor. such that the glass frit particles have a mean size at least five to 100 times greater than that of the photoconductive particles, and where the largest size of the glass particles is less than one half the resolving capability of the intended development system, with the glass frit being present in an amount from about to 99 percent by volume and said photoconductor particles present in an amount from about 1 to 25 percent by volume,

. coating said mixture onto a supporting substrate to form a binder layer in which substantially all of the photoconductive particles are dispersed within the interstices of said larger glass frit particles, and

c. heating said layer to fuse said glass frit particles into a substantially homogeneous matrix whereby said photoconductor particles are trapped in said glass matrix in the form of a plurality of continuous paths through the thickness of said glass binder layer.

2. The method of claim 1 in which the size of the largest size glass particles are about 16 microns.

3. The method of claim 1 in which the size of the largest size glass particles are about 12 microns.

4. The method of claim 1 in which the size of the largest size glass particles are about 35 microns.

5. The method of claim 1 in which the size of the largest size glass particles are about 25 microns.

6. The method of claim 1 in which the size of the largest size glass particles are about 4 microns.

7. The method of claim 1 in which the glass frit particles in the particulate mixture are present in a size distribution from about 0.1 to 70 microns and the photoconductor particles have a size distribution of from about 0.001 to 2.0 microns.

8. The method of claim 1 in which the glass frit particles in the mixture have a size distribution from about 1 to 10 microns and the photoconductor particles have a size distribution from about 0.001 to 1 micron.

9. The method of claim 8 in which the mean or average particle size of glass frit is at least five times greater than than of the photoconductor particles.

10. The method of claim 1 in which the photoconductor particles in the particulate mixture are present in an amount from about 3 to 15 percent by volume and the glass frit binder particles in an amount from about to 97 percent by volume.

11. The method of claim 1 in which the particulate mixture of glass frit and photoconductor particles is formed as a slurry with a carrier liquid in which neither material is soluble, and which is evaporated to form a dried binder layer prior to fusing the glass particles.

12. A glass binder layer which is made by the method of claim 1.

13. The method of claim 1 in which the glass frit particles have a mean size at least 100 times greater than that of the photoconductive particles. 

2. The method of claim 1 in which the size of the largest size glass particles are about 16 microns.
 3. The method of claim 1 in which the size of the largest size glass particles are about 12 microns.
 4. The method of claim 1 in which the size of the largest size glass particles are about 35 microns.
 5. The method of claim 1 in which the size of the largest size glass particles are about 25 microns.
 6. The method of claim 1 in which the size of the largest size glass particles are about 4 microns.
 7. The method of claim 1 in which the glass frit particles in the particulate mixture are present in a size distribution from about 0.1 to 70 microns and the photoconductor particles have a size distribution of from about 0.001 to 2.0 microns.
 8. The method of claim 1 in which the glass frit particles in the mixture have a size distribution from about 1 to 10 microns aNd the photoconductor particles have a size distribution from about 0.001 to 1 micron.
 9. The method of claim 8 in which the mean or average particle size of glass frit is at least five times greater than than of the photoconductor particles.
 10. The method of claim 1 in which the photoconductor particles in the particulate mixture are present in an amount from about 3 to 15 percent by volume and the glass frit binder particles in an amount from about 85 to 97 percent by volume.
 11. The method of claim 1 in which the particulate mixture of glass frit and photoconductor particles is formed as a slurry with a carrier liquid in which neither material is soluble, and which is evaporated to form a dried binder layer prior to fusing the glass particles.
 12. A glass binder layer which is made by the method of claim
 1. 13. The method of claim 1 in which the glass frit particles have a mean size at least 100 times greater than that of the photoconductive particles. 